AVR-Chat

--- In AVR-Chat@yahoogroups.com, "Chuck Hackett" <egroupscdh@...> wrote:

> By "disable verification", I assume
> you mean turning off LPM in the
> application section ...

No.  In your original post, you wrote (in part):
>> For a "hostile" environment (to protect the code):
>> (snip)
>> LB: Programming & verification disabled

I rather thought that once you have taken this step it is no longer possible to read the Flash via the SPI and JTAG interfaces.  Thus, it is safe to leave either or both enabled so that you can rescue a device if necessary by erasing it (which also prevents the Flash contents from being read by destroying it).

The following may not be what you want, but for information this is how I set the lock bits in the AVR ICE-Cube and other products with Flash loaders for field-update of firmware:

Mode 3:
- Further programming and verification disabled
Application Protection Mode 1:
- No lock on SPM and LPM in Application Section
Boot Loader Protection Mode 3:
- LPM and SPM prohibited in Boot Loader Section

My reasoning as as follows:

Mode 3 prevents the Flash contents from being read using any of the programming interfaces (SPI, JTAG, High-Voltage).

Boot Loader Protection Mode 3 prevents someone from writing an application that reads and dumps the Flash loader program.

If anyone can think of a way (short of high-effort die breaking) that either the Flash loader or the application could be read with these settings, I'd appreciate the heads up.

Graham.